Preheat your oven to 350°F (175°C) and prepare a muffin tin with liners.

In a large mixing bowl, combine canned pumpkin puree, melted butter, granulated sugar, egg, and vanilla extract. Mix until smooth.

In a separate bowl, whisk together all-purpose flour, baking soda, baking powder, salt, and ground cinnamon. Gradually add to the pumpkin mixture.

Mix the melted butter, brown sugar, and ground cinnamon in a small bowl for the cinnamon swirl.

Fill muffin cups halfway with pumpkin batter, add a spoonful of cinnamon swirl, then top with more batter.

Swirl the cinnamon mixture gently into the batter with a toothpick.

Bake for 20-25 minutes, checking for doneness with a toothpick.

Whisk together powdered sugar, vanilla extract, and milk for the glaze while muffins bake.

Cool muffins for 5 minutes before transferring to a wire rack and drizzling with glaze.